During the court hearings, the eldest told how he beseeched another hiker to call emergency services toward the end of a 19-mile trek on Aug. 28 — reportedly when the temperatures reached 108 degrees.

He had been throwing up, falling down because of cramping, and experiencing vision changes.

"I needed medical attention and I was hurting and he was hitting and pushing me and calling me fat," he told the court.

"I was scared and it was hard and I was all weak and tired and kind of hurt."

The boys' paternal grandmother, Pam Beatty, told ABC that each of the boys had lost between 20 and 30 pounds.

In sentencing Carlson to the minimum term available, US District Judge Frederick Martone said he obviously cared for his grandchildren and noted that he had struggled with attention-deficit disorder and hyperactivity his entire life.

He had his first child — Tara Danaher, the mother of his three grandsons — when he was 15 and in all had five children by five different mothers.

Danaher was 17 when her eldest was born.

According to Reuters, Carlson told investigators that his grandsons were out of shape and that he just wanted to make them tougher and more physically fit.

He told the court that he had wanted to show his grandchildren the beauty of the Grand Canyon, and he'd never intended to hurt them.

"I love my grandchildren greatly," said Carlson, who was shackled at the hands and ankles for his court appearance.

"I wanted to afford these children a beautiful opportunity at a young age to experience something magnificent."

However, ABC cited court paperwork as saying that when the boys' mother arrived in Arizona to collect them, the park ranger keeping an eye on the situation while waiting for other rangers to arrive found Carlson to be "intimidating, controlling and would not allow her to speak with the boys."

A ranger also reported seeing Carlson shove one of the boys 13 times.

Having already served nearly 10 months, Carlson may only have another 11 months to serve.

Carlson's attorney, Jeffrey Williams, also told Reuters that he would appeal the sentence.